Use MPI_Init_thread if OpenMP is enabled

ls1mardyn / ls1-mardyn

ls1-MarDyn is a massively parallel Molecular Dynamics (MD) code for large systems. Its main target is the simulation of thermodynamics and nanofluidics. ls1-MarDyn is designed with a focus on performance and easy extensibility.

http://www.ls1-mardyn.de

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Use MPI_Init_thread if OpenMP is enabled #306

Open cniethammer opened 4 months ago

cniethammer commented 4 months ago

If MPI is used in a multi-threaded environment the MPI implementation has to be aware of the calling context of MPI methods. Therefore, initialize the MPI environment with MPI_Init_thread requesting the desired thread support level. So far ls1 makes MPI calls only from the main thread, i.e., uses MPI_THREAD_FUNNELED. For details see the MPI standard.

cniethammer commented 4 months ago

Based on the feedback and diving deeper into the MPI standard, I refactored this PR.

Note:

The logging infrastructure is not available at this point in the code. Therefore mardyn_exit() cannot be used, because it uses the Logger internally.
I replaced MPI_Init() with MPI_Init_thread() entirely now. The MPI standard says here 'A call to MPI_INIT has the same effect as a call to MPI_INIT_THREAD with a required = MPI_THREAD_SINGLE." (MPI 4.1 p.486)